The present invention relates to localized radiation therapy and devices therefore. More particularly, the present invention is directed to radiation delivery devices using palladium-103, and to their methods of manufacture.
Radioactive materials have long been used in the medical treatment of diseased tissues. Such radioactive materials may be implanted into a patient at the site of the diseased tissue or may be locally applied externally through the skin. In either case, it is desirable to have the radioactive material in a form which will permit it to be used to irradiate the diseased tissue while minimizing damage to nearby healthy tissue. Therefore, it is desirable to have a radiation delivery device which will uniformly irradiate a diseased area with a controlled dosage of radiation while minimizing the exposure of surrounding healthy tissue to the radiation.
Interstitial implantation of radiation delivery devices for localized tumor treatment has long been recognized. The advantages of interstitial implants reside in their ability to concentrate the radiation in a localized area thereby minimizing radiation exposure to nearby healthy tissue. Commonly used implantable radioactive materials include iridium-192, iodine-125, gold-198 and radon-222. However, each radiation source type has limitations. For instance, most of these isotopes emit high energy gamma rays and the energy of their X-ray radiation is relatively low. Also, some of these isotopes have relatively long half-lives which make them less desirable for brachytherapy treatments.
Several types of radioactive implants are known from U.S. Pat. No. 5,342,283 (Good). This patent discloses radioactive implants such as microspheres, wires and ribbons coating with radioactive metals by, for example, sputtering. The radioactive implants disclosed in this patent are solid, seamless elements which may be individually implanted or combined in intercavity applicators with fabrics and in ribbons. A variety of different radioisotopes are disclosed.
U.S. Pat. No. 4,323,055 (Kubiatowicz) discloses a radioactive iodine seed wherein the carrier for the radioisotope is a rod-like member which is detectable by x-rays and occupies a substantial portion of the space within the seed. The radioactive iodine is distributed on the carrier body using an ion exchange process by first halogenating the carrier body and then conducting an ion exchange reaction with the radioactive material. Alternatively, the radioactive iodine can be electroplated onto the carrier body. The carrier body is placed within a biocompatible container such as a titanium capsule for use.
U.S. Pat. No. 5,713,828 (Coniglione) discloses a brachytherapy device formed from a hollow tube-shaped seed substrate which allows association of the device with suture material to prevent migration of the device in the body. The radioactive material is distributed on the exterior surface of the tubular device to provide a relatively uniform radiation field around the brachytherapy seed source. A tubular, biocompatible outer casing is placed around the inner, radioactive tube to seal the radioactive material within the device. A variety of radioactive materials are disclosed for use with the device.
In addition to the above mentioned radioactive materials, it is also known to use palladium-103 in radiation therapy. Generally, Pd-103 does not suffer from the high energy gamma radiation problems associated with the previously mentioned isotopes. Consequently, irradiation treatments employing Pd-103 radiation can be more localized than with other radioactive isotopes thereby reducing the potential for harm to nearby healthy tissue.
U.S. Pat. No. 4,702,228 describes therapeutic seeds containing Pd-103 prepared by increasing the Pd-102 or content found in palladium metal, i.e., by enriching palladium metal in Pd-102 or content and then by exposing it to a neutron flux in a nuclear reactor so as to convert a small fraction of the Pd-102 into Pd-103. Alternatively, Pd-104 enriched palladium can be employed in which case the Pd-104 will be exposed to proton bombardment to produce radioactive Pd-103.
Generally, palladium-103 is produced in a nuclear reactor by bombarding a target containing Pd-102 with neutrons (Pd-102(n,xcex3) Pd-103). Since all of the Pd-102 nuclei are not converted and, since in addition, other naturally occurring isotopes of the element palladium are typically present in small amounts in the target, Pd-103 cannot be produced in a carrier free state. By carrier-free state it is meant Pd-103 containing substantially no other palladium isotopes. Since there are small amounts other isotopes of Pd present in the target, neutron activation products of these isotopes are produced as well. For example, the reaction Pd-108(n,xcex3)Pd-109 also occurs and therefore Pd-103 obtained from a reactor by neutron bombardment always contains a small amount of the radioisotope Pd-109. Since Pd-109 is the same element as Pd-103, no chemical means are known to effect their separation. The presence of other nuclides of Pd in the target also leads to the production of significant amounts of certain non-Pd radioisotopes, e.g. if radioactive Pd-111 is produced, it will decay to another radioactive isotope, Ag-111, further complicating the radiochemical purification of the Pd-103 matrix. In contrast, Pd-103 produced in a particle accelerator, such as a cyclotron, may be obtained in a carrier-free state, i.e. containing substantially no palladium isotopes other than Pd-103.
Another drawback of radiation delivery devices produced in a nuclear reactor from Pd-102 enriched palladium is that for practical reasons soon to be apparent, one is obliged to use reactor grade Pd-103 at the specific activity level generated in the reactor. This places significant limitations on the level of dosage that can be delivered by a device which employs reactor grade Pd-103. In contrast, cyclotron-produced carrier-free Pd-103 can be employed in a way that provides for its economical utilization while at the same time providing for a device having a predetermined therapeutic or apparent activity.
The specific activity of Pd-103 that can be produced in a nuclear reactor is determined by the level of enrichment of the Pd-102 target used, the neutron flux in the reactor and the length of exposure of the target to the neutron flux in the reactor. Generally, the highest enrichment of Pd-102 available (Oak Ridge National Laboratories (ORNL)) has an isotopic purity of 77.9% Pd-102 with the remaining 22.1% of the target being made up of the other isotopes of Pd. The highest neutron flux available in the world is found in the ORNL HFIR facility where the level is approximately 2.6E 15 neutrons/cm2 sec. This reactor runs in 21 day cycles with approximately 10 days between cycles. Due to the generation of extraneous isotopes such as Ag-111, the maximum practical irradiation time is two cycles. These factors taken together indicate the maximum specific activity that can be derived from a nuclear reactor target is approximately 345 Ci/g. In contrast, the specific activity of carrier-free Pd-103 can be as high as 75,000 Ci/g.
As such, smaller amounts of carrier-free Pd-103 can be employed in radiation delivery devices as compared to reactor grade Pd-103 in order to achieve the same level of activity. Additionally, a greater degree of control over the specific activity of a particular device can be exercised when using carrier-free Pd-103 since the only potential error factors which enter into this process are the measurement of the specific activity of the carrier-free Pd-103 and the provision of the right amount for the desired level of specific activity in the device. Therefore, for these reasons it is often preferably to employ carrier-free Pd-103 in radiation delivery devices.
U.S. Pat. No. 3,351,049 to Lawrence et al. suggests the use of carrier-free palladium-103 in therapeutic seeds. U.S. Pat. No. 5,405,309 to Carden, Jr. also discloses the use of carrier-free Pd-103 in therapeutic seeds wherein carrier-free Pd-103 is mixed with a small amount of palladium metal, electroplated onto a pellet of electroconductive material, and encapsulated within a biocompatible container. By virtue of the electroplating and encapsulating procedures, a certain degree of self-shielding was observed which affected the efficacy and potency of the therapeutic seeds. However, such procedures were deemed necessary for proper containment of the radiation source material. Further, the therapeutic seeds disclosed in these patents are somewhat limited in use by their rigid physical dimensions.
In view of the above, there has remained a need in the art for versatile radiation delivery devices which exhibit reduced self-shielding properties while effectively containing the radiation source material.
It is an object of certain embodiments of the present invention to provide radiation delivery devices comprising a substrate and a radiation source material adhered to the outer surface of the substrate or incorporated into the substrate, wherein the radiation source material comprises carrier-free Pd-103. A variety of different types of substrates may be employed depending primarily upon the particular application for which the device will be employed.
It is a further object of certain embodiments of the present invention to provide methods for deposition of a radiation source material onto a substrate.
It is yet another object of certain embodiments of the present invention to provide a radiation delivery device, wherein the substrate design, and/or the radiation source material configuration is such that the device may provide a non-uniform, i.e. directional, radiation distribution.
It is another object of certain embodiments of the present invention to provide a radiation delivery device comprising a substrate and a radiation source material deposited onto, or incorporated into the substrate, wherein the substrate is shaped to fill a body cavity and the radiation source material comprises palladium-103.
It is a still further object of certain embodiments of the present invention to provide a method for filling a body cavity with such a radiation delivery device.